A navigation system performs travel guidance for enabling a user to easily and quickly reach the selected destination. A typical example is a vehicle navigation system where the user drives the car having the navigation system. Such a navigation system detects the position of the vehicle, reads out map data pertaining to an area at the current vehicle position from a data storage medium, for example, a CD-ROM (compact disc read-only memory), a DVD (digital versatile disc), or a hard disc, and displays a map image on a monitor screen while superimposing a mark representing the current location of the user vehicle on the map image. Alternatively, such map data can be provided to the vehicle from a remote server through a communication network such as Internet.
When a destination is set, the navigation system starts a route guidance function for setting a guided route from the starting point to the destination. To determine the guided route to the destination, the navigation system calculates and determines an optimum route to the destination based on various parameters. For example, the guided route is determined based on the shortest way to reach the destination, the route preferring freeways to surface roads, the least expensive way to the destination, or the route without using toll road, and the like.
Typically, the route guidance function performs an intersection guidance process in which a monitor screen displays an enlarged intersection diagram and the direction in which the vehicle is to travel while displaying the guided route on a map. During the route guidance, the navigation system reads the nodes data from the data storage medium such as DVD and successively stores the nodes data of street segments (expressed in longitude and latitude) constituting the guided route in a memory.
During actual traveling, the node series stored in the memory is searched for a portion of the guided route to be displayed in a map display area of the monitor screen, and the portion of the guided route is highlighted so as to be discriminable from other streets. When the vehicle is within a predetermined distance of an intersection it is approaching, an intersection guidance diagram (an enlarged or highlighted intersection diagram with an arrow indicating the direction in which the vehicle is to turn at the intersection) is displayed to inform a user of the desired one of roads or directions selectable at the intersection. Such route guidance by the navigation system is also given by voice instruction.
There is a type of navigation system having a function that accepts two or more destinations. Sometimes, such a function is called a “Today's Plan” mode or a “Trip Itinerary” mode in which a user can specify two or more destinations and the order of the destinations. Typically, the navigation system detects the arrival of the current destination based on the address number on the street segment. Then the navigation system displays the address and/or the name of the destination to help the user find the exact location of the current destination such as one within a shopping mall.
After the detection of arrival at the current destination, at some point, the navigation system must proceed to show the next destination and start the route guidance to the next destination by calculating an optimum route to the next destination. However, it is difficult for the navigation system to know when the user would want to proceed to the next destination. Thus, a conventional technology incorporates a manual input means such as a “Next Destination” key which is so designed that the user activates the key when proceeding to the next destination.
FIG. 1 summarizes the foregoing procedure involving the “Next Destination” key. In the flow chart of FIG. 1, the navigation system calculates the route to the first destination and guides the user to the first destination at step 21. The navigation system measures a distance to the first destination, and when the distance is within a predetermined range, it generates an arrival notice at step 22. When the user has achieved the purpose at the first destination and wants to move to the second destination, he presses the “Next Destination” key of the navigation system in step 23.
Accordingly, at step 24, the navigation system determines the guided route to the second destination and guides the user to the second destination. Thus, the procedure similar to the above is repeated for the second destination. Namely, the navigation system measures a distance to the second destination, and when the distance is within the predetermined range, it generates an arrival notice at step 25. When the user has achieved the purpose at the second destination and wants to move to the third destination, he presses the “Next Destination” key of the navigation system to proceed to the third destination at step 26. In this manner, the procedure is repeated for the remaining destinations.
The above procedure involving the manual input means is cumbersome to the user because the user has to press the “Next Destination” key every time when the route guidance to the next destination has to be started. Without the manual input means, on the other hand, the conventional arrival detection method alone may prematurely display the next destination when the user still has not arrived at the actual destination. This is because the conventional detection method is affected by the limited accuracy of the map database. It is also possible that the navigation system does not show the next destination in a timely manner even if the user no longer has to stay at the current destination.